Acrylonitrile polymerization in the presence of ion-exchange resin having-so3h groups



United States Patent I 3,395,133 ACRYLONITRILE POLYMERIZATION IN THEPRESENCE OF ION -EXCHAN GE RESIN HAV- ING S0 H GROUPS Gaetano F.DAlelio, South Bend, Ind., assignor of twentyfive percent to Walter J.Monacelli, Cleveland, Ohio N0 Drawing. Continuation-in-part ofapplication Ser. No. 249,342, Jan. 4, 1963. This application Aug. 8,1966, 7 Ser. No. 570,744

10 Claims. (Cl. 26088.7)

ABSTRACT OF THE DISCLOSURE I This invention comprises an improvedprocess for the production of substantially colorless polymers ofacrylonitrile by polymerization in organic solvents capable ofdissolving polymers containing at least 60% of acrylonitrile and even80% or more acrylonitrile, this polymerization being effected by freeradical mechanism in the presence of an insoluble, isolable, infusibleion-exchange resin having SO H groups therein. Removal of theionexchange resin leaves a solution of colorless acrylonitrile polymerthat is resistant to discoloration after spinning or shaping into fibersor film, etc., even upon aging or heating, such as for example at 150 C.

This application is a continuation-in-part of pending application Ser.No. 249,342, filed Jan. 4, 1963, now abandoned.

This invention relates to an improved method for solution polymerizationof acrylonitrile. More specifically it relates to a method ofpolymerizing acrylonitrile in various organic solvents in whichacrylonitrile polymers containing at least 60% acrylonitrile, and evencontaining 80% acrylonitrile or more, are soluble. Still moreparticularly, this improved process results in the production ofsubstantially colorless acrylonitrile polymer solutions from whichsubstantially colorless films and fibers can be cast or spun.

The current commercial method of producing acrylic fibers comprise anumber of expensive steps. Usually, acrylonitrile, alone or with one ormore comonomers is polymerized in a water solution or emulsion fromwhich the polymer is removed by filtration, washed, dried, ground ormilled and finally dissolved in a solvent, then refiltered to give adopecontaining about of the polymer which is extruded into fibers by eitherwet or dry spinning methods.

In order to avoid the additional steps of recovering polymer and thendissolving the separated polymer in a solvent to prepare the polymersolutions for spinning, it is desirable to prepare the polymer in situby polymerizing the acrylonitrile, together with any desired comonomers,in the solvent and to use the resultant solution of the polymer directlyas the spinning solution. However, such a process has not beenconsidered feasible for a numberof reasons, such as the highradical-transfer coefiicient of the types of solvents usually requiredto dissolve the polymers.

Furthermore, prior to the present invention, it has been foundimpractical to conduct the acrylonitrile polymerizations in suitablesolvents since color formation results (1)during the solutionpolymerization and/or (2) on drying the polymer spun or case fromsolution and/or (3) heat treating the dried polymer.

The presence of initial color in the acrylonitrile polymers is highlyundesirable since this interferes with subsequent application of dyes.Where light colored dyes are to be applied, the results are entirelyunsatisfactory when color is present in the original polymer. While somesmall 3,395,133 Patented July 30, 1968 amounts of color can be toleratedor compensated for when dark colored dyes are to be applied, substantialamounts of color are highly undesirable since they cause somewhaterratic dyeing in view of the variations of color in the polymer andalso because corresponding degrees of dyeing in such cases are difficultto reproduce. Moreover, the adjustment for this initial color inthepolymer is highly unsatisfactory in that more careful control andinspection in the application of the dye are required; and even in suchcases the color matches are poor.

On the other hand, when the color of the original fiber is very lightbut discoloration occurs during further drying or heat pressing orironing, the value of the fibers or the textile produced therefrom isgreatly reduced. Therefore, it is highly desirable that theacrylonitrile polymer be produced in a colorless or, at most, apractically colorless condition. Heretofore this has not been possiblein the desired technique of preparing the acrylonitrile polymer in situby solution polymerization. It is also important that the heat stabilityof the acrylic polymers and copolymers obtained during thepolymerization, whatever their original color, possess the highestresistance to thermal discoloration.

It is an object of this invention, therefore, to produce substantiallycolorless solutions of acrylonitrile polymers and copolymers which canbe spun or extruded into desired shapes and to produce polymers ofimproved therrnal resistance to discoloration. Other objectives of thisinvention will become apparent as the description of the inventionproceeds.

The objectives of this invention are achieved by the preparation ofpolymers of acrylonitrile containing at least 60 and preferablyacrylonitrile by means of solution polymerization, in the presence ofisolable, insoluble, infusible sulfonated ion exchange resins, of asolution containing 2050%, preferably 2635% by weight of acrylonitrile,together with any comonomer or comonomers, based on the total weight ofthe solution, at a temperature in the range of 30-60 C., preferably 4050C., until a conversion of at least 10%, preferably at least 30-40% ormore of monomer to polymer having an average molecular weight of atleast about 50,000 has been effected. The ion exchange resin is morefully described hereinafter.

While the time necessary to effect such minimum conversion dependssomewhat on the temperature, the amount.

of catalyst and the concentration of monomer, satisfactory resultsgenerally are obtained Within a reaction time of 10-50v hours.

It is desirable in preparing acrylonitrile polymer and copolymersolutions that such solutions be ungelled. In solution polymerization ithas been found that when substantial amounts of monomer have beenconverted to polymer, gelation or precipitation of the polymer occurs.The term gelation as used herein means that a solution has become soviscous that there is no free flow. In such cases, prolonged heating andagitation are required to reconvert the gel to a fiowable solution.

The degree of conversion of monomer to polymer at which gelation orprecipitation occurs, will vary according to the particular solventbeing used, the temperature of the solution, and the presence of anycomonomers which tend to make the resultant polymer 'more soluble. Withall other factors equal, homopolymers of acrylonitrile will reachgelation at a lower degree of conversion than in the case ofacrylonitrile copolymers. With comonomers which contribute to thesolubility of the copolymers, a higher degree of conversion can be ef-'fecte'd before gelation is reached. Likewise, as the amount of comonomercontributing to solubility is increased, a greater degree of conversionis permitted before gelation.

The following table illustrates the effect of additional TABLE I PartsParts Percent Acrylo- Methyl Conversion nitrile Acrylate at GelationHowever, since the properties of the polymer are affected by the amountof comonomers present, the use of comonomer to permit increasedconversion is limited. If dilute solutions of the monomer portion areused in order to permit higher degrees of conversion, the molecularweights are adversely affected. Acrylonitrile polymers having molecularweights below about 30,000 generally are not spinnable. At molecularweights of about 35,000, the polymers are spinna-ble but cannot bestretched uniformly without breaking. Above molecular weights of 35,000spinnability and stretchability are improved and the elongation, tensilestrength, loop strength, etc. of the spun fiber increase gradually withincreased molecular weight of the polymer. Generally molecular weightsabove 40,000 and for most commercial purposes, molecular weights above50,000 are preferred.

Therefore, in order to produce acrylonitrile polymers of a desiredmolecular weight, it is necessary to avoid the use of dilute solutionsof the monomer portion. Generally, the lower limit of monomerconcentration is that which will permit production of the desiredmolecular weight, and the upper limit is determined according to thedegree of conversion that will cause gelation.

When the degree of conversion that can be tolerated in a certainpolymerization system is being approached, the addition of acrylonitrilemonomer or even other monomer, or other non-solvent materials, willcause precipitation of the polymer.

The above molecular weights are average molecular weights. Whenpolymerization is started, a higher concentration of monomer is present.Therefore the polymers produced at that time have a relatively highermolecular weight than are produced in later stages of thepolymerization. For example, for a particular polymerization in whichthe product has an average molecular weight of 50,000, a polymerproduced at the beginning of the polymerization may have a molecularweight of 70,00080,000'. Then at the end of the polymerization,depending upon what degree of conversion is attained, the molecularweight may be 20,000 or even lower. Therefore, it dilute solutions ofmonomers are used initially, there is a shift downward through the wholemolecular weight range, thereby making it necessary to stop thepolymerization at a low degree of conversion in order to obtain anaverage molecular weight in the desired range.

Very often it would be desirable to add initiator at later stages ofpolymerization to continue polymerization and also to shortenpolymerization time in reaching the desired degree of conversion. As theinitiator is used up there are fewer free radicals generated. However,if larger amounts of initiator are added at the beginning of thepolymerization, this larger amount contributes to the production oflower molecular weight polymers. Where it would be desirable to addadditional amounts of initiator in later stages of the polymerization,as pointed out above, the initiator is a non-solvent material andtherefore such addition when the degree of conversion of monomer topolymer is approaching the maximum that can be tolerated in thesolution, will cause precipitation or gelation.

Moreover, the monomer portion, including both the acrylonitrile monomerand any .comonomers, is a nonsolvent for acrylonitrile polymers havingabout or more of acrylonitrile therein. Therefore, the proportion ofmonomer to solvent that can be used in a solution polymerization systemis also limited. In addition to this effect of monomer on the solubilitycharacteristics of solution polymerization, it is desirable also toremove unconverted monomers before spinning since its presenceintroduces a somewhatv variable factor in the spinning operation. If thepolymer solution is to be stored before spinning, it is likewiseimportant to remove unconverted monomer since polymerization maycontinue with resultant gelation during storage. Therefore, it isdesirable to have as high a degree of conversion as possible withoutadversely affecting the polymer properties in order to reduce the amountof monomer that needs to be removed and thereby the cost of suchremoval.

For example, a solution of 0.5 part of polyacrylonitrile inv parts ofdimethyl formamide can tolerate the addition of 100 parts of acetonewithout precipitation of the polymer. However, if a second addition of10 parts of acetone is made, the polymer will precipitate.

In another case, if a solution of 3 parts of polya-crylonitrile in 97parts of dimethyl formamide has 15 parts of acetone added thereto, thepolymer is precipitated.

In another instance, a solution containing 5 parts of poly-acrylonitrilein'95 parts of dimethyl forma-mide has polymer precipitated when 5 partsof acetone are added.

For a solution of 22 parts of poly-acrylonitrile in 100 parts ofdimethyl formamide, 1 part of acetone is more than enough to precipitatethe polymer.

In corresponding experiments using acrylonitrile monomer in place of theacetone, similar results are obtained. For example, with a solution of0.5 part of polyacrylonitrile in 78 par-ts of dimethyl formamide, theaddition of 78 parts of monomer does not precipitate the polymer.However, a total of parts of monomer will precipitate the polymer.

It appears that the maximum concentration of polyacrylonitrile indimethyl formamide is approximately 22 percent by weight at 50 C. Thismeans that if polymerization is conducted at 50 C. with 30%acrylonitrile in dimethyl formamide, gelation or precipitation ofpolymer will occur when about 50% of the monomer has been converted topolymer because of the presence of the unconverted monomer.

It is undesirable to carry the polymerization to such a high degree ofconversion that there is a risk of causing gelation. Once gelation hasoccurred, it is a difficult, timeconsuming and expensive operation toheat and stir the resultant gel in order to get it back into workablesolution. In order to avoid this, solution polymerizations are generallycarried only to a degree of conversion that is a safe distance away fromthe gelation point.

The foregoing disadvantages are overcome when the solutionpolymerization is initiated under the various conditions most favorabletoward obtaining the desired molecular weight and thereafter addingsolvent in one or more increments, with or without additional initiatorprior to the gelation stage. The amount of solvent to be added by suchincremental addition will vary according to the particularpolymerization system and the results desired. For example, the moreinsoluble the resultant polymer and the greater degree of conversionsdesired, the smaller will be the amount of solvent added in eachincrement and the greater will be the number of incremental additions.In contrast, the more soluble the polymer and the lower the degree ofconversion required, the greater will be the amount of solvent that canbe added per increment and the fewer such additions will be necessary.

Any solvent which will dissolve acrylonitrile polymers having at least80% acrylonitrile therein can be used in the practice of this invention.It is only necessary that the solvent is a liquid at the temperature atwhich polymerization is conducted and that the solvent'is reasonablystable under polymerization conditions. Any number of such solvents havebeen disclosed in Patents Nos. 2,407,714 through 2,407,727 inclusive.Typical of these solvents which can be used in the practice of thisinvention, include but are not restricted to the following:

N,N,N,N' tetramethyl-alpha-ethylamalonamide;N,N,N,N'-tetramethylglutaramide; N,N,N',N-tetramethylsuccinamide;Thiobis-(N,N-dimethylacetamide) Bio(N,N-dimethylcarbamylmethyl) ether;N,N,N',N'-tetramethylfumaramide; Methylsuccinonitrile;

1,2,3-tricyanopropane; Alpha-ethylsuccinonitrile;

Succinonitrile; N,N-dimethylcyanoacetamide;N,N-dimethyl-beta-cyano-propionamide; Dimethylester of methanedisulfonic acid; Diethylester of ethane-1,2-disulfonic acid;Bis-(cyanomethyl -sulfone;

1,2-dithiocyanopropane; Bis-(thiocyanomethyl) ether;Beta-thiocyanoisobutyronitrile; S-hydroxy-Z-piperidone;3-hydroxy-2-pyrrolidone; N-formyl-piperidine; N-formyl-pyrrolidone;2,2,2,2'-tetra-amino-5,5'-dimethyl-diphenylmethane; Nitronaphthol;

Dimethyl sulfoxide;

Tetramethytlene sulfoxide; Pentamethylene sulfone;N,N-bis-(cyanomethyl)formamide; N,N'-diformyl-piperazine;N,N-dimethylmethoxyacetamide; N,N-dimethylcyanamide;

Glycolonitrile;

Hydracrylonitrile;

Malonitrile.

Any free radical enerating initiator or catalyst suitable forpolymerization of acrylonitrile by solution polymerization is suitablefor the practice of this invention. The amount of such initiator orcatalyst used at the beginning of the polymerization is the amountnormally used for solution polymerization. The preferred types ofcatalyst are perand azocatalysts. Typical catalysts suitable for thepurpose of this invention, include but are not restricted to thefollowing: various persulfate compounds such as potassium persulfate,sodium persulfate, etc.; various peroxy compounds such as benzoylperoxide, acetyl peroxide, lauryl peroxide, phthalyl peroxide,tetrahydrophthalyl peroxide, succinyl peroxide, naphthyl peroxide,t-butyl perbenzoate, hydrogen peroxide, ditertiary butyl diperphthalate,acetyl-benzoyl peroxide, etc., 2,2-azobisisobutyronitrile, etc. Whensuch initiators are added in the solvent additions there isadvantageously at least about 0.05% based on the weight of monomer andpreferably between 0.1 and 1.0%. Larger amounts, even up to 5%, can beused provided that the resultant lower molecular weight of the polymeris desired or can be tolerated.

In preparing acrylonitrile polymers for spinning into fiber, or forforming film, or for various other uses for which solutions ofacrylonitrile polymers can be used, it is generally desirable to havepresent in the polymer at least 0.1 and as much as of one or morecomonomers which improve the solubility and dyeability characteristicsof the acrylonitrile polymer and to facilitate processing of the polymersolution and the ultimate shaped article. Various typical comonomerswhich have been found useful for this purpose are listed hereinafter.

Of particular usefulness for improving the solubility characteristicsare the methyl, ethyl, propyl and isopropyl acrylates. In the presentinvention methyl and ethyl acrylates are preferred because they areinexpensive, easily available, polymerize easily with the acrylonitrileand with other comonomers, etc. Most important, however, is the factthat the methyl and ethyl acrylates have polymerization rates close tothe ideal polymerization rate for effecting a uniform composition in theresultant copolymer. In other words, their polymerization rates areclose to that for acrylonitrile and, therefore, the two monomerscopolymerize in such a manner as to give a substantially uniformcopolymer composition.

Typical preferred comonomers for improving the solubility include thefollowing, which can be used individually or in combination of two,three or more comonomers: methyl acrylate and its homologs, namely theethyl, propyl, butyl and amyl acrylates; the correspondingmethacrylates, namely methyl, ethyl, propyl, butyl, and amylmethacrylates; vinyl acetate, vinyl propionate, vinyl buty rate, vinylvalerate; dialkyl itacon'ates, maleates and fumarates, the alkyl groupsbeing similar or different and preferably lower alkyl groups, i.e.containing no more than 5 carbon atoms, such as dimethyl itaconate,diethyl maleate, methyl amyl itaconate, ethyl butyl fumarate, diamylitaconate, etc.; vinyl chloride, vinylidene chloride, vinylidenecyanide, alpha-methacrylonitrile, alpha-ace-toxy-acrylonitrile, vinylaryl compounds, such as styrene, vinyl naphthalene, and vinyl diphenyl,the corresponding alpha-methyl derivatives, and the nuclear-substitutedderivatives thereof in which the nuclear substituents are chlorine,fluorine, acetoxy, and alkyl groups, said alkyl and acetoxy groupspreferably having no more than 5 carbon atoms therein. Such substitutedvinyl aryl compounds can have one or more substituent groups of the typeindicated thereon, either of the same or dilferent types, but it isgenerally preferred that no more than two such substituent groups beattached to an aromatic nucleus.

Typical examples of such substituted vinyl aryl comonomers are:

vinyl toluene,

ethyl styrene,

propyl styrene,

butyl styrene,

amyl styrene,

dimethyl styrene,

diethyl styrene,

methyl ethyl styrene,

methyl amyl styrene,

chloro styrene,

fluoro styrene,

dichloro styrene,

dicluoro styrene,

methyl chloro styrene,

methyl fluoro styrene, trifiuoromethyl styrene, acetoxy styrene,acetoxy-methyl styrene,

chloro acetoxy styrene,

vinyl methyl naphthalene, vinyl chloro naphthalene,

vinyl fluoro naphthalene,

vinyl ethyl naphthalene,

vinyl dimethyl naphthalene, vinyl diethyl naphthalene, vinylmethyl-chloro naphthalene, vinyl amyl naphthalene,

vinyl methyl butyl naphthalene, vinyl acetoxy naphthalene,alpha-methyl-styrene, alpha-methyl-vinyl toluene, alpha-methyl-vinylethyl benzene, alpha-methyl-vinyl chloro benzene,

7 alpha-methyl-vinyl methyl naphthalene, alpha-methyl-vinyl chlorotoluene, alphaernethyl-vinyl acetoxy naphthalene, alpha-methyl-vinyldiphenyl, isopropenyl methyl diphenyl, isopropenyl chloro diphenyl,isopropenyl methyl diphenyl, isopropenyl dimethyl diphenyl, isopropenylbutyl diphenyl, etc.

While the above comonomers are particularly preferred for forming moresoluble and more easily workable acrylonitrile copolymers, various othercomonomers can be used in preparing'copolymers of acrylonitrile inaccordance with thepractice of this invention, including higher alkylderivatives of the various esters and vinyl aryl compounds listed above,as well as corresponding aryl and cycloalkyl derivativesi Variousothercomonomers, such as acrylamides and methacrylamides, bothunsubstituted and substituted with various all-:yl aromatic andcycloalkyl groups, as well as various other c-omonomers shown in theprior art can also be used.

Any reasonably accurate method of determining molecular weight can beused. However, the method used in determining molecular weights in theabove examples is as follows: a solution of about 0.5% by weight ofpolymer or copolymer is made in dimethyl formamide, and the viscositymeasured at 20 C. in an Ostwald Viscometer, and recorded at t the timeof flow in minutes. The time of fiow in minutes, t for the pure dimethylformamide solvent is also measured; and the specific viscosity 1 isgiven as (t z )/t from which the molecular weight is calculated from therelationship 1 =M-K-C., wherein K has a value of 1.5 X 10*. C equals thenumber of grams of polymer per liter divided by the molecular weight ofacrylonitrile, and M is the molecular weight.

The percent of polymer conversion is easily determined by weighing out aquantity of polymer solution in a small beaker, allowing the greatportion of the solvent and unconverted monomer to evaporate, to form afilm, then drying to constant weight and thereafter weighing the driedpolymer film. Knowing the original proportion of monomer in thesolution, and the weight of dried film dried from a given weight ofsolution, it is possible to determine the percent of polymer resultingfrom the starting amount of monomer. Alternately the polymer solutionmay be precipitated, as for example, with water, the polymer isolated byfiltration and dried to constant weight and the conversion calculated.

In most cases it is desirable to perform polymerization of acrylonitrileand mixtures thereof with various comonomers in an oxygen-free or inertatmosphere. In such cases inert gases such as nitrogen, carbon dioxide,neon, helium, hydrogen and methane are particularly suitable as inertblanketing media for this purpose.

The process of this invention lends itself very conveniently tocontinuous operation as well as batch polymerization and spinning. Incontinuous operation, the residence time for effecting polymerization inthe proper temperature zone can be controlled by adjusting the flow rateof the polymerization solution in accordance with the size of the vesselor zone in which the temperature is properly maintained for effectingpolymerization.

The resultant polymer solution can then be flowed directly into thespinning apparatus or can be cooled to retard further polymerization andand thus stored until desired for spinning. However, a preferredprocedure is to remove unpolymerized monomer from the solutions bydistillation processes and the resulting stable solution used directlyor stored for future use. Alternately, the solution can be allowed topolymerize to high conversion simultaneously with further addition ofsolvent with or without more initiator until substantially a 100%conversion is obtained.

In the present invention, the polymerization is performed, at leastinitially, in the presence of an ion exchange resin as describedhereinafter, till at least about 10% and preferably 20% of the monomerhas polymerized, up to complete conversion of the monomer to polymer, ifdesired. The polymerization may be performed in a single reactor, withor without agitation, or in a series of reactors, with or withoutagitation in each reactor. For example, the first stage can be performedin an agitated reactor until'1520% conversion is achieved, and the sec0nd stage can be performed in a column type reactor without agitationand without or with packing, such as glass beads, Rachig rings, etc. inwhich case the packing can comprise cation exchange resin in bead orgranular form to function also as part of the packing. The spinningtechniques and further processing and use of the polymers of thisinvention can be effected in accordance with standard procedures usedfor such processes and products.

The ion exchange resins used in the practice of this invention areinsoluble crosslinked' sulfonated polymers, having free 'SO H group,preferably attached directly to an aromatic ring such as the benzene,toluene, etc. rings. The ion-exchange resins used for this purpose mustbe insoluble so as to be easily separated from the solution of theacrylonitrile polymer. Otherwise if the ion-exchange resin is solubleand thereby retained in the acrylonitrile polymer it will eventuallycause discoloration, particularly upon heat treatment of the finalproduct.

One of the best known cation exchange resins is the class of sulfonatedaminoalkenyl-polyalkenyl copolymers, such as the sulfonatedstyrenedivinyl benzene copolymer described in my US. Patent 2,366,007,December 26, 1944. Other cation exchange resins which can be used in thepracticeof this invention are disclosed in my US. Patents 2,366,007,December 26, 1944; 2,628,193, February 10, 1953; 2,631,127, March 10,1953; 2,644,801, July 7, 1953; 2,645,621, July 14, 1953; 2,684,387,August 24, 1954; as well as the earlier known phenol-sulfonicacidaldehyde type cation exchange resins. Other classes of sulfonic acidtype cation exchange resin can be used, such as those disclosed in myUS. Patent 3,068,190, issued December 11, 1962, derived from thecondensation of aldehydes and triazines containing an aldehyde reactablegroup and sulfonated aryl group attached to the triazine ring. Thoughthe sulfonic group, -SO H, in the resins used in the practice of thisinvention is preferably attached directly to an aromatic structure, itcan be attached to an aliphatic moiety such as in the crosslinkedcopolymers of vinyl sulfonic acid emon sour}u or vinyl benzyl sulfonicacid,

etc., though such polymers are less desirable and more expansive thanthose in which the SO H group is attached to an aromatic ring.

In the practice of this invention, the polymers are prepared in solutionin the presence of the insoluble, crosslinked sulfonic acid type polymerand before isolation of the polymer such as by spinning, casting orprecipitation, the ion exchange resin is completely removed from thepolymer. The ion exchange resins used in the practice of this inventionare preferably in a form which permits their removal from the reactionmixture by filtration or by centrifuging, or as a fixed bed in a reactorvessel or a column. These ion exchange resins can be in the form ofbeads, granules, ground powders, films, filaments, or fibers, etc. Theseinsoluble, crosslinked sulfonated cation exchange resins, used in thepractice of this invention, are ineffective when the -SO H group isneutralized, such as when their K, Li, Na, Ca and Mg salts are used, andalso actually induced more color when their ammonium and amine salts areused. It is a requirement, therefore,

that a substantial amount, that is, 25% or more of the sulfonic groupsbe in the hydrogen or acid form, SO H. 1

Normally, the commercial resins are more readily available in the saltform, fiSO Na, from which the free acid is readily regenerated bytreatment with inorganic acid by well-known procedures. 1

The use of cation exchange resins containing fre SO H groups in thepreparation of the polymers'of this invention, is not equivalent to, andis not to be confused with, the addition of free H 80 to the polymersolution; nor is it equivalent to the addition of other inorganic acidssuch as HCl, H P O.,, etc. The reasonfor this is not completelyunderstood, but it may be that the free acids react in small amountswith the acrylonitrile or its polymer to give either coloredderivatives, or colorless derivatives which, under the infiuenceofmoderate or high temperatures, decompose to produce colored derivatives.i v

I The 'sulfonated cation exchange resins differ markedly from the freeacid since the free acid also influences the polymerization unfavorablyby lowering its rate and decreasing the molecular Weight in proportionto the amount of sulfuric acid used, and at higher concentration causeserious color formation, as compared to solution from which the acid isomitted. On the other hand, there .is substantially no decrease inpolymerization rate or mo: lecular weight when an equivalent or excessweight of ion exchange resin is used. Moreover the presence of thesulfonated cation exchange 'resin has the added benefit of providing amarked improvement in 'freedomfrom color (1) of the solution, (2) of theinitial isolated dried polymer, and (3) of the final polymer even whenheated for 30 minutes or even 1 hour at 150 C., as illustratedhereinafter in the examples.

It is advantageous to use at least 0.1 part of said resin per 100 partsof solution. Preferably the ratio of monomer portion to solvent portionin said solution is 3035:65'-70 respectively, in which monomer portionat least 80%- by weight is advantageously acrylonitrile.

Generally the degree of sulfonation of the resin is not critical, sincelarger amounts of resin having a smaller degree of sulfonation can beused in place of smaller amounts of resin having a higher degree ofsulfonation. However, for practical purposes, it is desirable to useresins having at least 0.1% by weight. of sulfonic acid groups therein,advantageously 1% and preferably at least3%. v

Useful fibers and films can be made from the solutions of the polymersand copolymers of this invention by dry spinning, as in the preparationof cellulose acetate fibers,

orby wet spinning, as in the preparation of viscose rayon.

In wet spinning, the solution of the polymer or copolymer can be spuninto a substance which is a non-solventforthe copolymer, but which isadvantageously compatible with the solvent in which the copolymer isdissolved. For example, water, acetone, methyl alcohol, carbondisulfide, glycerine, chloroform, carbon tetrachloride, benzene, etc.,may be used as a precipitating bath for dimethyl formamide, N,N-dimethylacetamide, butyrolactone, ethylene carbonate, dimethyl sulfoxide, andother solvent compositions of these polymers. The extruded fibers, fromwhich substantially all of the solvent has been removed inthe spinningstep, about ll0 percent remaining in the shaped article, can then becold-drawn about 100900 percent, preferably about 300-600 percent; andthe drawn fiber heat-treated, usually at substantially constant length,at about 100-180 C., to effect further crystallization and re moval ofthe remaining solvent. The term heat-treated, as used herein, refers tothe application of heat to an object, usually at a controlledtemperature and-usually by means of the medium, either liquid orgaseous; surrounding theobject.

The invention is best illustrated by the following examples. Theseexamples are intended merely for purposes of illustration and are not tobe regarded as limiting the scope of the invention in any way. Exceptwhere specifically indicated otherwise in the examples and throughoutthe specification, parts'and percentages are given as parts by weightandflpercentages by weight. Moreover, unless specifically indicatedotherwise, the term polymer is intended to include copolymers.

EXAMPLE I Q g Polymer A A mixtureof:

. Parts Monomerconsisting of 329 parts of acrylonitrile and 2.10 partsof methylaciylate 35 Distilled dimethyl formamide 65Azo-bis-isobutyronitrile 0.4

The procedure for preparing Polymer A is repeated using the polymerizedmixture of Parts Monomer mixture consisting of 32.9 parts ofacrylonitrile and 2.1 parts of methylacrylate 35 Distilleddimethylformamide 65 Azoisobutyronitrile n 0.4 H 80 (98%) 0.15

At the end of six hours the conversion is 33.4% and the averagemolecular weight of the polymer is 98,000; at the end of twenty-fourhours the conversion is 84.5% and the average molecular weight is70,200. The solution has a light yellow tint.

"Polymer C The procedure of Polymer B is repeated using the same mixtureof monomers with 0.3 part (98%) H instead of 0.15, part and theconversion at the end of twenty-four hours is 80.3% and the averagemolecular weight is 62,400.. The polymer solution is almost colorless.

1' Polymer D The procedure of Polymer B is repeated using 0.6 part of98% H 80 instead of 0.15 part and the conversion in 24 hours is 71.2%and the molecular weight is 51,300.

- The polymer solution has a distinct yellow color.

EXAMPLE II The procedures for Polymers IB, IC, and ID are repeated usinga commercial cation exchange resin (Dowex "'50)"which is sulfonateddivinylbenzenestyrene in the Molecular Polymer Parts Ion Ex- Percentchange Resin Conversion Weight;

118 0. 3 88. 4 76, 900 HO 0.6 88.2 77,100 IID 1. 2 88. 1 77, 600

EXAMPLE III Films are cast from the polymer solutions of Examples I andII by. first diluting the solutions with dimethyl formamide to 25%polymer solids, filtering the solution and casing the solutions on cleanglass plates followed by drying at room temperature for 4 to 6 hours,and a 1 1 50 C. for 12 hours. The films are then immersed in two changesof distilled water for 2 hours in each change of water, and then driedin a vacuum oven at 70-80 C. for 812 hours, and the color of the filmsobserved and hours and the solution filtered to remove the ion exchangeresin, yielding a polymer solution with an 80% conversion, and a polymermolecular weight of 74,300, which is then distilled at 15 mm. pressureto recover 4 parts of compared. The dried films are then heated in anair oven acrylonitrile, leaving a clear colorless solution of the polyat150 C. for 30 minutes and the color of the films mer in DMF solvent,which can be used as such, for the observed and compared. In all casesthe polymers prepreparation of the films and fibers or which may beconpared in the presence of the cation exchange resins are centratedfurther to higher solids content by removal of superior in color andheat resistance in comparison with DMF under reduced pressure to yield a22-25% polymer the polymers prepared with sulfuric acid or with solublesolution. polystyrene sulfonated resin or without either acid or EXAMPLEVII cation exchange resin This example illustrates the fact that the useof the ion zi g g gliggi fi 3: 3:5 :52: j i gi 2; exchange resin is animprovement not only over sulfuric H so dis 1 d1 p acid, but also overother acids such as HCI, H PO 2 4 co or very a y, ex ibitmg a browncolor, HCOOH CH COOH etc a 3 s whereas those prepaied 1n the presence ofion exchange A mixture resin are colorless. Parts EXAMPLE IV Dimethylformamide 260 Polymer A Acrylonitrile 131.6 A mixture of: Ethylmethacrylate 5.4 Parts 2,2-azobisisobutyronitrile 1.6 Dlmethyl formamlde(32'9 parts of acrylomtnle and is prepared and divided into four equalportions, a, b, c,

n of methylilcrylate) 65 and d, to which is added respectively 2,2-azobisisobutyron1tr1le 0.4 s i styrene lfo t 4 20 Part (a)0.3 part ofglacial acetic acid 50, 9 3 Part (b)0.7 part of cone. HCl (36.6%) Part(c)0.3 part of HCOOH 15 prepared under an inert atmosphere 1n a reactionflask Part 0 part of H PO and polymerized at 55 C. for 13 hours with aconverl 3 4 sion of 50.3% and a molecular weight of 71,000. The and themlxtures polylilenzed at r 22 hours- In Solution was light yellow incolor, Producing colored all cases colored solutions were obtained incontrast to dried films which disColored on heating polymers obtainedwhen the ion exchange is used in the mixture, as shown in the precedingexample. Polymer B Part A of this procedure is repeated using 0.6 partEXAMPLE VIII of Dowex 50 cation exchange resin in hydrogen form Thisexample illustrates the difference between the use instead of theequivalent 0.3 part sulfuric acid yielding of the ion exchange resins inthe practice of this invention a colorless solution with a conversion of58.9% and a and other acids using hydrogen peroxide as apolymerizamolecular weight of 76,600; the solution is colorless as tioninitiator. are the dried and heated films. 40 A mixture of: P

arts EXAMPLE v Dirnethyl formamide 175 A mlxture Acrylonitrile 70.5Acrylonitrue 2; M yl ryi 4. Ethylmethacrylate 2.1 H202 (90% soln')Dimethyl tormamide 65.0 is prepared and divided into five equalportions, a, b, c, d, Azoisobutyronitrile 0.4 and e, to Which is addedrespectively the following in- Itaconic anhydridc 0.4 gredients, and themixture polymerized at C. for Dowex 50 (H form) 0.6 10 hours.

Portion Substance Added Conversion, Molecular Color percent Weight 1part H2804 32 41, 000 Light yellow. 1 part H1170; low. 1 part SiCh. 1part H2 13. 5 42,100 Very yellow 1 part GHgCOOH allow. a 2 parts Dowex50 acid form.. 50. 6 61,000 Colorless 1N0 polymer. 1 and polymerized bythe procedure of Example I at 50 EXAMPLE IX C. for 13 hours, yielding a58.1% conversion with a A mixture of: molecular weight of 62,000; andthe solution is colorless. Parts When 0.3 part of soulfuri-c acid areused instead of the Dimethyl sulfoxide 35 ion exchange resin in thisprocedure a yellow colored Acrylonitrile 14 polymer solution is obtainedand the conversion, in the Ethyl acrylonitrile 1 same period of time, isreduced to 47.4% and the molecu- 2,2'-azobisisobutyronitrile 0.2 larweight lowered to 54,000. H 80 (98%) 0.5

is heated in a suitable stirred reactor at 50 C. for 11.2

is prepared in an inert atmosphere in a suitable reactor and heated at50 C. for 21.5 hours yielding a yellow colored solution with aconversion of 70% and a molecular weight of 52,800. When the sulfuricacid is replaced by 1 part of H 50 the color becomes more intense andmolecular weight is 49,600 with a conversion of 63.7%. However, when thesulfuric acid is replaced by 1 part of cation exchange resin in acidform, the conversion is 84% in 20 hours and the molecular weight is79,500.

I 7 EXAMPLE X A mixture of: I

. .wz 1 N Parts Dirnethylsulfoxide I 35.0 Acrylonitrile 14.1 Methylmethacrylate 0.9 11292 J. L. .2 L L Acetic anhydride 1.2 Dowex 50 resinin acid form 3.0 ,*To yield acetyl peroxide in situ.

is prepared under an 'inert atmosphere in a suitable reactor and heatedat 50 C. for hours to give a colorless solution'with a 58.2% conversionand a molecular Weight of 92,000. When 3 parts of H 80 are used insteadof the ionexchange resin, a.yellow colored solution is obtained.

1 EXAMPLEXI lThe procedureof Example X is repeated using 0.2 partsoflauroyli peroxide instead of the acetyl peroxide yielding a:49.2-%conversion at 50 C. with a molecular weight of 295,000. The use, of.H SOas in Example X instead Qf-theuiOr'rexchange resin lowers'the molecularweight to 9.2g000-and the conversion to 42.6% and produces a yelloWsolution of polymer.

. EXAMPLE XII A mixture of v Parts Acrylonitrile"f' 48.88 Ethyl acrylate2.12 Dimethyl forrnamide 148.0

is prepared and divided into three equal portions a, b, and,"'to'which1is added respectively g V Portion (a 0.1 part K 850 +0.5part Dowex 50 in acid Portion (b)0.05 part K S O +0.5 part Dowex 50 in md o ln. a. Portion (c)-0.'025 part K S O +05 part Dowex 50 in acid formA in suitable reaction vessels under a deoxygenated nitrogen atmosphereand reacted at 40 C..for 47 hours with the followingconversion,.molecular weight and color:

Color Portion Conversion, Molecular percent Weight 5s 75; 000 Colorless.55 78,000 D0.

.. 50 I 7 89,000 Do.

I h EXAMPLE XIII A mixture of Parts Dimethyl for'mamide 35 Acrylonitrileu 14.1 Propyl'ac'r ylatenw 0.9 Benz o yl peroxide a 0.5 Dowex resin inacid form "2.0

is prepared ina suitable reactor under an inert nitrogen atmosphere andheated at 45 C. for 24 hours, yielding a 95% conversionwith a molecularweight of 62,000 in substantially colorless solution. When H 804 issubstituted for the ion exchange resin a colored solution of molecularweight of 45,400 is obtained.

-EXAMPLE XIV "The procedure of Example XIII 'is repeated using 0.69 partof tertiary'but'yl peroxide instead of 0.5 part of benzoyl peroxide."'At- 29% conversion the molecular weight'is93,300 and the solution iscolorless.

Similar results are obtained, also, when the tertiary butyl peroxide isreplaced by 0.49- of tertiary butyl hydroperoxide. 7

EXAMPLE XV LExampleuI is-repeated ,using instead of'dimethyl formamide,65 parts of dimethyl acetamid-e and the conversion at the'end of .12hours is 49.8%,. and the molecular weight is 76,200; the polymersolution is colorless.

1.4 EXAMPLE XVI Example I is repeated using instead of dimethyl form;amide, 65 parts of butyrolactone and the conversion at the end of 14hours is 50.1% and the molecular weight is 72,480.

EXAMPLE XVII A mixture of V Parts Acrylonitrile 329 Ethyl acrylate 21Dimethyl formamide 650 2,2'-azobisisobutyronitrile 4 Sodium styrenesulfonate 3 Dowex- 50 ion exchange resin (H form beads) 6 are reacted ina stirred vessel in a deoxygenated atmosphere at 50 C. for 11 hours'to'a conversion of approximately 60%, and a polymer molecular weightof'77,100, following which the pressure is reducedto 120 mm. and 143parts of unreacted monomer, substantially all acrylo nitrile, removed bydistillation, leaving a solution of 214 parts polymer in 650 parts ofsolvent. The solution is then filtered to remove the ion exchange resinand is wet spun into a glycerine bath; cold-drawn at a ratio of 8:1,washed with water and dried. Colorless fibers With excellent heatresistance, when heated at 150 C. for 30 minutes, and excellentdyeability are obtained. Similar properties are obtained when thespinning bath consists of a mixture of water and dimethyl formamide, orwhen the solution is dry-spun.

' EXAMPLE XVI-II Example XVII is repeated with the exception that thecation exchange resin is removed from the solution at the end of threehours polymerization time at 50 C. with a conversion of 19.8% and thepolymerization continued for an additional 8 hours in the absence of theresin but in a deoxygenated atmosphere. The color of the fibers isalmost identical to the fibers of Example XVII with only a slight tintevident in large masses of the massesof the fiber which is in contrastto the markedcolor resulting when Example XVII is repeated in theabsence of the ion exchange resin throughout its entire polymerizationcycle.

EXAMPLE XIX To a tube, 2'' ID. and 3 feet long, filled with a mixture ofglass beads of 0.2 mm. and Dowex 50 ion exchange resin beads 0.15 mm.diameter in a weight ratio of :5, and equipped with thermostatic meansfor maintaining the temperature at 50 C., an inlet pump and port, andoutlet port and outlet pump, is swept out with deoxygenated nitrogen andthen continuously fed with a deoxygenated solution in which the ratio ofcomponents is Parts Dimethyl formamide 6500 Acrylonitrile 3290 Ethylmethacrylate 210 Sodium styrene sulfonate 25 2,2-azobisisobutyronitrile40 at a rate so that the residence time is 12 hours resulting in apolymer solution with a conversion of 60% and a molecular weight of76,800 at the outlet port from which the solution is transferred bymeans of the outlet pump through a filter into a flash evaporator,maintained at 50-55" C. and -130 mm. which removes unreacted monomer,accumulating a polymer solution similar to that of Example XVII fromwhich fibers and films are spun continuously.

EXAMPLE XX The procedure of Example IIB is repeated under pressure of-130 p.s.i. at 50 C. using 35 parts of mono- 15 mer mixture with thefollowing monomer compositions in percent by weight:

Polymer Acrylonitrile, Vinyl chloride,

percent percent 5 EXAMPLE XXI The procedure of Example XX is repeatedusing the following monomer composition:

Acrylonitrile, Vinyl chloride, Methacrylonitrile,

percent percent percent Polymer and colorless solutions eminentlysuitable for the preparation of films and fibers are obtained.

Generally, polymers containing at least 80% acrylonitrile are consideredas suitable for the preparation of fibers of suitable physicalproperties and solvent resistance. As generally now well-known, thesolvent resistance of copolymers that contain one or more monomer unitsin addition to those formed by the acrylonitrile is atfected by the typeand proportion of copolymerizing monomer or monomers used to replacepart of the acrylonitrile. For example, copolymers can contain variousproportions of such monomer units as obtained from vinylidene chloride,methacrylonitrile, tumaronitrile, and betacyano methyl acrylate, withoutconsiderable reduction in solvent resistance.

Replacement of acrylonitrile units in the copolymers by vinyl chloride,styrene and alpha-methyl-styrene units results in copolymers of loweredsolvent resistance, the amount of such lowering in resistance in eachcase depending on the amount substituted. In addition to the solventresistance, certain other physical properties of the copolymers areaffected by the presence of these additional units in the copolymers.The amount and character of the changes in physical properties of thesecopolymers depend again on the type and proportion of copolymerizingmonomer or monomers used. For example, the tensile strength of anacrylonitrile copolymer will decrease much more when one or moremonomers have relatively weak secondary bonding forces, such as styreneor ethylene is used to replace part of the acrylonitrile than when oneor more monomers having relatively strong bonding forces, such asmethacrylonitrile, fumaronitrile, methyl beta-cyano-acrylate andvinylidene chloride, is used to replace part of the acrylonitrile.Moreover, the ability of these copolymers to form molecularly orientedshaped articles depends on the type and amount of the copolymerizingmonomer or monomers used to replace acrylonitrile.

In the field of high polymers, molecular orientation is usuallyindicated and identified by birefringence or polarized light, as underNicol prisms, by increased density as compared to the density of thesame polymer unoriented, and by characteristic X-ray difiractionpatterns. When a material is crystalline or oriented, its X-ray diagramshows bright areas or spots for points of crystallization and dark areasfor the non-crystalline regions. The intensity or number of these brightspots increases with the degree of orientation or crystallization.Amorphous or non-crystalline materials give X-ray diagrams having veryfew highlights or bright spots Whereas crystalline or oriented materialsgive definite X-ray diffraction patterns. In these patterns there aredefinite relationships 16 of the bright spots with regard to positionand spacing which are generally characteristic of the composition of thematerial being X-rayed. In fibers or films the orientation usuallyfollows the direction of drawing or stretching so that the orientationis parallel to the fiber axis or a major surface.

Many of the acrylonitrile copolymers of this invention can bemolecularly oriented, especially if there is no more than 20 percent ofanother monomer or mixture of monomers in the copolymer molecule. Thisis true when the major portion of the copolymer is acrylonitrile, forexample, 80 percent or more acrylonitrile, or when the othercopolymerizing monomers used in making such copolymers have substituentgroups, having secondaryvalence bonding forces equal to or greater thanexhibited by the cyano group in acrylonitrile. For example, if suchmonomers as methacrylonitrile, fumaronitrile, vinylidene chloride, andmethyl betacyano-acrylate are used wtih acrylonitrile, the proportion ofacrylonitrile in the copolymers can be much less than 80 percent withoutdestroying the capacity for molecular orientation.

Accordingly, many molecularly oriented, cold-drawn, shaped articles ofparticular usefulness are prepared from copolymer compositionscontaining in the polymer molecules about only 60 percent acrylonitrile,with or without one or more monomers of the class consisting ofvinylidene chloride, vinyl chloride, styrene, alpha-methyl styrene,methacrylonitrile, fumaronitrile, beta-cyano-dimethyl-acrylamide, andmethyl beta-cyano-acrylate, etc.

EXAMPLE XXII The procedure of Example HE is repeated using parts ofmonomer mixture with the following composition in percent by weight:

Polymer Acrylonitrile, Styrene, Furnaryl N itrile,

percent percent percent and clear colorless solutions are obtained fromwhich fibers and films are obtained, which can be molecularly orientedby cold-drawing.

In place of styrene, various styrene derivatives can be used, such asalpha-methyl styrene; nuclearsubstituted chloro-styrenes, i.e., ortho-,rneta-, and para-chloro-styrenes, dichloro-styrenes, for example, the2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dichloro-styrenes,trichloro-styrenes, cyano-styrenes, such as ortho-, meta-, andpara-cyanostyrenes, dicyano-styrenes; nuclear-substitutedalkyl-styrenes, such as monoand di-methyl-styrenes, rnonoand diethylstyrenes, monoand di-isopropyl styrenes; arylsubstituted styrenes, i.e.,para-phenyl-styrene, etc., cycloaliphatic-substituted styrenes, such aspara-cyclohexylstyrene; fluoro-styrenes such as ortho-, meta-,para-fluorostyrene, difiuoro-styrenes, etc.; trifiuoro-methyl-styrene,such as ortho-, meta-, and para-trifluoromethyl-styrenes,di(trifiuoromethyl)-styrenes, and various other styrenes or mixtures ofany number of these with each other or with styrene.

EXAMPLE XXIII The procedure of Example II is repeated with similarexcellent results using in place of the Dowex ion exchange resinequivalent amounts respectively of:

(a) A sulfonated phenol-formaldehyde resin;

(b) A formaldehyde resin condensation product of a triazine compound ofthe formula (c) A divinyl benzene crosslinked copolymer of vinylsulfonic acid; and

(d) A divinyl benzene crosslinked copolymer of vinyl benzylsulfonicacid.

Very small amounts of the ion exchange resins are effective in thepractice of this invention, with at least 0.1 part of ion exchange resinper 100 parts of solution being most practical. Since excessiveproportions of resin do not have any adverse efiects there is no upperlimit on the proportion of resin except as determined by practicallimitations. When solutions are runthrough fixed beds of such resin inthe practice of this invention the ratio of resin to solution can bevery high.

While the present invention is particularly advantageous in thepreparation of polymers having at least 60 percent of acrylonitrile,especially so with those having 80 percent or more acrylonitrile,because of the solubility and gelation problems, it has also been foundthat the practice of this invention has advantages, e.g., in avoidingcolor formation with acrylonitrile copolymers having as little as 25percent acrylonitrile.

While such copolymers having these low proportions of acrylonitrile,e.g., 2530%, can be prepared with little or no color by the use ofsulfuric acid, subsequent heat treatment of the resultant polymerscauses discoloration. However, this subsequent discoloration is avoidedwhen these copolymers are prepared in the presence of cation exchangeresins as described herein.

While certain features of this invention have been described in detailwith respect to various embodiments thereof, it will, of course, beapparent that other modifications can be made within the spirit andscope of the invention, and it is not intended to limit the invention tothe exact details shown above, except insofar as they are defined in thefollowing claims:

The invention claimed is:

1. A process for the free radical solution polymerization ofacrylonitrile to solid polymers color stable at 150 C. comprising thestep of polymerizing at a temperature of EEO-60 C. a monomer portioncontaining at least 60 percent by weight of acrylonitrile therein, saidmonomer portion comprising 25-50% by weight of the combinedmonomer-solvent dissolved in an organic solvent capable of dissolvingacrylonitrile polymers containing at least 60 percent by weight ofacrylonitrile in the polymer molecule thereof, in the presence of atleast about 0.1 part by weight to 100 parts by weight of solution an 18insoluble, isolable, infusible ion-exchange resin having at least 0.1%by weight of free SO H groups therein to a conversion of at least 10percent by weight of the monomer to polymer and before reachinggelation, and thereafter separating the ion-exchange resin from theresultant polymer solution.

2. The process of claim 1 in which said monomer proportion contains atleast 80 percent by weight acrylonitrile and said solvent is capable ofdissolving polymers having at least 80 percent by weight ofacrylonitrile in the polymer molecule thereof.

3. The process of claim 2 in which the monomer solution contains 2635%by weight of monomer based on the total weight of monomers and solvent.

4. The process of claim 3 in which the polymerization is conductedwithin the temperature range of 40 to C.

5. The process of claim 4 in which said ion-exchange resin has at least1% by weight of free SO H groups therein.

6. The process of claim 5 in which the polymerization is performed inthe presence of a free radical generating catalyst.

7. The process of claim 6 in which the solvent is dimethyl formamide.

8. The process of claim 6 in which the solvent is dimethyl acetamide.

9. The process of claim 6 in which the solvent is dirnethyl sulfoxide.

10. The process of claim 7 in which the free radical generating catalystis 2,2-azobisisobutyronitrile.

References Cited UNITED STATES PATENTS 2,794,793 6/1957 Coover 260-88.7

FOREIGN PATENTS 871,279 6/ 1961 Great Britain.

JOSEPH L. SCHOFER, Primary Examiner.

HARRY WONG, JR., Assistant Examiner.

